Oxygen Vacancies in β-MoO3 Mediate Imine Synthesis via Reductive Coupling of Nitro Compounds and Alcohols.

Organonitrogen chemicals with C=N bonds are one of the most important groups of chemicals with broad applications, but their synthesis via reductive coupling remains a great challenge, because of the favorable hydrogenation of C=N bonds into C-N bonds. In this study, a nitrogen-doped carbon-supported β-MoO3 catalyst with abundant oxygen vacancies (Ov) was discovered to be robust in the reductive coupling of nitro compounds with biomass-derived alcohols toward the synthesis of organonitrogen chemicals, including imines and N-heterocycles with C=N bonds. The Ov in β-MoO3 serves a crucial role in the adsorption and activation of substrates via the electronic interaction between the negatively charged oxygen atoms in these substrates and the Ov sites in β-MoO3. The presence of Ov greatly lowers the energy barriers of the reductive coupling reaction, and the electron transfer from alcohols to nitro compounds is mediated by the Mo5+/Mo6+ redox cycle. Our method demonstrates excellent selectivity to C=N bonds and is effective for a wide substrate scope including the highly inert methanol and ethanol. This study highlights the use of non-noble metal oxides as alternatives to traditional metal nanoparticles for various challenging organic transformations.